1.Field of the Invention
The invention relates to a joint socket for a hip endoprosthesis.
2.Description of the Related Art
In the case of total hip endoprostheses, a prosthesis stem having a joint head is inserted into the femur. A joint socket, which serves as a bearing shell for the joint head, is implanted in the pelvic bone. It is known to construct the joint socket from a socket shell and a socket insert. The socket shell can be optimised with regard to implantation in the pelvic bone, whereas the socket insert can be optimised with regard to the bearing properties for the joint head. In that case the socket shell is so formed and so positioned in the pelvic bone as to allow ingrowth that is as stable as possible by the socket shell in the pelvic bone. The socket insert can be oriented in the socket shell in such a way that the joint head is accommodated so that the prosthesis stem and accordingly the femur of the patient are as far as possible in the correct orthopaedic position.
From EP 0 663 193 A1 there is known a joint socket wherein the socket insert has a spherical outer surface and that spherical outer surface is seated in a spherical accommodating space—of the same spherical radius—of the socket shell. Therefore, when the socket insert has been inserted into the socket shell, the socket insert can be rotated at will about its axis of rotation and its axis of rotation can be tilted at will with respect to the axis of rotation of the accommodating space. As a result, it is possible for the socket shell to be positioned in the pelvic bone in accordance with the bone structure. The socket insert can be oriented in accordance with the orthopaedic position of the prosthesis stem inserted into the femur. In order to fix the socket insert in its position within the socket shell, the inner spherical surface of the accommodating space of the socket shell has pointed projecting teeth which engage in the outer surface of the socket insert. Because the teeth have to dig into the outer surface of the socket insert, there are limitations with respect to the choice of material for the socket insert. Pressing the socket insert onto the teeth of the socket shell makes it difficult for the socket insert to be inserted in a precisely positioned manner.